Lithium batteries, particularly, lithium secondary batteries, have characteristics such as high energy density and long lifespan, and therefore, the lithium batteries are widely used as power supplies for electric appliances such as video cameras, portable electronic devices such as notebook computers and mobile telephones, electric tools such as power tools, and the like. Recently, the lithium batteries have been also applied to large-sized batteries that are mounted in electric vehicles (EVs), hybrid electric vehicles (HEVs), and the like.
The lithium secondary battery is a secondary battery having a structure in which, at the time of charging, lithium is eluted from the positive electrode as ions and moves to a negative electrode to be stored therein, and at the time of discharging, lithium ions return from the negative electrode to the positive electrode. It is known that a high energy density of the lithium secondary battery is caused by a potential of a positive electrode material.
As a positive electrode active material for these types of the lithium secondary batteries, there are known lithium metal composite oxides such as LiCoO2, LiNiO2, and LiMnO2 which have a layered structure and lithium metal composite oxides (in the invention, also referred to as “LMO”) such as LiMn2O4 and LiNi0.5Mn1.5O4 which have a manganese-based spinel structure (Fd-3m).
Among them, the manganese-based spinel-type lithium metal composite oxide (LMO) are produced from inexpensive materials, are non-toxic and safe, and have properties highly tolerant to overcharging, and therefore, attention has been paid as a next-generation positive electrode active material for large-sized batteries used for electric vehicles (EVs), hybrid electric vehicles (HEVs), and the like. In addition, since a spinel-type lithium metal composite oxide (LMO) that is capable of three-dimensional insertion and release of Li ions, has superior power output characteristics compared with the lithium metal composite oxide having the layered structure, such as LiCoO2, the spinel-type lithium metal composite oxide is expected to be useful in applications where excellent power output characteristics are required, such as batteries for EV and batteries for HEV.
With respect to the spinel-type lithium metal composite oxide (LMO), conventionally, for example, JP 2000-306577 A discloses a positive electrode active material for a nonaqueous electrolytic liquid secondary battery that is a lithium manganese oxide having a spinel-type crystal structure represented by a formula Li1+xMnMg1yAl2zO4 (where, x≥0, y, and z>0), the positive electrode active material having excellent high-temperature cycle characteristics or high-temperature storage characteristics in the nonaqueous electrolytic liquid secondary battery.
JP2000-323140 A discloses a positive electrode material for a nonaqueous electrolytic liquid secondary battery characterized by being obtained in such a manner that a part of Mn in a spinel structure represented by a composition formula LiMn2O4 is substituted with at least one selected from Li, Na, K, Co, or Al and at least one selected from Mg, Ti, Cr, Fe, or Cu, and obtained in such a manner that a part of O (oxygen) is substituted with F (fluorine), wherein a lattice constant “a” is equal to or less than 8.22 Å, a specific surface area is 0.8 m2/g or less, and a mean valence of Mn is 3.7 or less.
JP2000-331682 A discloses a positive electrode material for a lithium secondary battery which is a Li—Mn composite oxide having a spinel structure obtained in such a manner that a part of cations in the spinel structure represented by a composition formula LiMn2O4 is substituted with at least one selected from Na, K, Co, Al, Mg, Ti, Cr, Fe, Cu, or Ni, and one or both of occupancy (gc) of the cations in a unit lattice determined from a composition, a lattice constant, and a density and occupancy (ga) of anions in a unit lattice determined from a composition, a lattice constant, and a density are characterized by being 0.985 or less.
WO 2009/054436 A (WO 2009/054436 A1) discloses a spinel-type lithium metal composite oxide (LMO) in which both power output characteristics and charge-discharge cycle ability during a high-temperature cycle can be balanced, wherein an inter-atomic distance Li—O is defined to be 1.971 Å to 2.006 Å as measured by the Rietveld method using a fundamental method in a lithium metal composite oxide represented by a general formula Li1+xM2-xO4 (where M is a transition metal including Mn, Al and Mg and x is 0.01 to 0.08).
WO 2010/114015 A (WO 2010/114015 A1) discloses a positive electrode active material for lithium battery that can increase a filling density, can increase power output characteristics, and has a low voltage drop during storage in a state of being charged at a high temperature, the positive electrode active material for lithium battery including a spinel-type (Fd-3m) lithium metal composite oxide represented by a general formula Li1+xM2-xO4-δ (where M represents a transition metal including Mn, Al and Mg, x represents 0.01 to 0.08, and 0≤δ) and a boron compound, wherein an inter the atomic distance Li—O of the spinel-type lithium metal composite oxide is 1.971 Å to 2.006 Å, and the amount of magnetic substance measured for the positive electrode active material for lithium battery is 600 ppb or less.
Upon considering a use for a battery mounted in electric vehicles (EVs), hybrid electric vehicles (HEVs), or the like, a spinel-type lithium metal composite oxide needs to have characteristics (referred to as “high-temperature storage characteristics”) capable of maintaining capacity even in a state of being stored at a high temperature, when being used as a positive electrode active material for a lithium battery.
Therefore, the invention is intended to provide a novel spinel-type lithium metal composite oxide having excellent high-temperature storage characteristics capable of maintaining capacity even in a state of being stored at a high temperature, when being used as a positive electrode active material for a lithium battery.